diffuser

or diffusor

(in various machines or mechanical systems, as centrifugal pumps or compressors) a device for utilizing part of the kinetic energy of a fluid passing through a machine by gradually increasing the cross-sectional area of the channel or chamber through which it flows so as to decrease its speed and increase its pressure.

3.

(in a lighting fixture) any of a variety of translucent materials for filtering glare from the light source.

4.

a pierced plate or similar device for distributing compressed air for aeration of sewage.